Hydrogeological investigation of the central part (central sub-basin) of the Erbil basin (north of Iraq)

The study area covers an area of about 1400 km², which is the central part of the Erbil Basin. The subject of the present thesis is to understand the current groundwater level in the aquifers (confined and unconfined aquifers) in the central part of Erbil Basin (central sub-basin), and to determine the possible factors for the fluctuations. The basin is caused by step sliding which in turn, causes the basin to hold more Quaternary deposits of more than 350 m making high productive aquifers. The annual rainfall is around 392 mm, of which 92% of this precipitation occurs from December to March. The statistical analyses showed the annual precipitation general trend is declining in contrast to a temperature which raised 1°C from 2001 to 2021. The morphometric analysis indicates homogenous deposits, materials subjected to weathering and erosion, high permeability, and low relief. Various methods have been applied to estimate the hydrogeological properties of aquifers. The groundwater levels in 24 wells that were located in the Erbil Central sub-basin were measured during one year by using a sounder. The hydraulic conductivity, transmissivity, and storage coefficient of the aquifers were calculated by using AQTESOLV software related to the results of pumping tests of 24 wells. Pumping test data of time-drawdown and well information shows the basin is dominant of unconfined system, while parts of the basin have locally confining beds. The transmissivity is ranged from 0.52 to 183.3 m²/d, the specific yield ranged from 0.088 to 0.281, the hydraulic conductivity is between 0.0027 to 1.1315 m/day, and the storage coefficient is between 0.0128 to 6.386. Long-term water table fluctuation showed a decline of the water table from an average of 62 m from 2001 to 2021 and showed that the middle of the area is more sensitive. A number of factors cause groundwater table fluctuations in the study area. The reasons are; (i) climate change has had a negative impact on the study area, (ii) variations in rainfall amount and pattern it has an impact on the amount of recharge water entering the groundwater, and (iii) if there is a long period between two dry periods, (iv) rain-fed crops will absorb a large portion of the incoming rainstorms that results the reducing of infiltrated rainwater percolation, (v) changes in land use due to urbanization, industrialization, agricultural lands, and (vi) leakage of groundwater flowing to adjacent basins or rivers, and (vii) excessive exploitation.